Process for anti-corrosive protection by reduction of ionised metals on metal substrate

ABSTRACT

Protecting iron and steel against corrosion by deposition of a metallic deposit from ionic compounds on the metal to be protected. The method comprises applying to the metal to be protected a paint consisting of at least one elemental metal of higher electrode potential than the metal to be protected, and at least one metal compound which yield metal ions of lower electrode potential than the metal to be protected or the elemental metal in organic binder, then treating the dry paint with acidic aqueous electrolyte containing at least one of said metal ions.

Wisniewski [451 Jan. 15,1974

PROCESS FOR ANTI-CORROSIVE PROTECTION BY REDUCTION OF IONISED METALS ON METAL SUBSTRATE Leonard Wisniewski, 302 Henley Manor, Beach Road, Moville Point, Cape Town, South Africa Filed: June 14, 1971 Appl. No.: 152,999

Inventor:

Foreign Application Priority Data June 17, 1970 Brazil 219822 US. Cl 117/62, 106/1, 117/130 R Int. Cl B44d l/44 Field of Search 117/50, 130 R, 62;

References Cited UNITED STATES PATENTS 9/1970 Golden 106/1 3,582,387 6/1971 Todd 106/1 Primary Examiner-William D. Martin Assistant Examiner lanyce A. Bell Att0rneyEmory L. Groff et al.

[57] ABSTRACT Protecting iron and steel against corrosion by deposition of a metallic deposit from ionic compounds on the metal to be protected. The method comprises applying to the metal to be protected a paint consisting of at least one elemental metal of higher electrode potential than the metal to be protected, and at least one metal compound which yield metal ions of lower electrode potential than the metal to be protected or the elemental metal in organic binder, then treating the dry paint with acidic aqueous electrolyte containing at least one of said metal ions.

8 Claims, No Drawings PROCESS FOR ANTI-CORROSIVE PROTECTION BY REDUCTION OF IONISED METALS ON METAL SUBSTRATE This invention relates to the protection of iron and steel against corrosion. More particularly, it relates to anti-corrosive protection by metallic film deposition from ionic compounds on a metal substrate and to the compositions from which said ionic compounds are deposited and the method in which the compositions are used.

In accordance with one aspect of the invention a protective metallic film deposition on a metal substrate is provided, which comprises application to the metal substrate of a coating of compounds capable of yielding ions of metals of higher and lower electrode potential than the metal substrate which is being protected.

Accordingto a further aspect of the invention, there is provided material suitable for coating over a metal surface to protect it against corrosion, which includes a dispersion of compounds capable of yielding ions of higher and lower electrode potential than the metal substrate upon action of an electrolyte, said compounds being dispersed in an organic binder.

These and other objects of the invention will be pointed out in the description of the invention which follows, or willbe apparent therefrom.

The compositions applied to the metal substrate which it is desired toprotect from corrosion comprise a mixture of materials in the following groups:

1. ionized metals;

2-. elemental metal;

3. solvent or liquid vehicle;

4. over-voltage reducing agent;

5. binder. t

The metal compounds (1)are those capable of yielding metal ionsand may be compounds of any ionizable element which is reducible by transfer of electrons from the metal (2) upon action ofan electrolyte bringing the metal compounds (I) in the composition into ionic contact with the metals (2) inthe composition.

Suitable metal compounds include the perchlorates, acetates, chlorides, carbonates or oxides of the metals or even the metals themselves, or their alloys in the form of fine powders.

The elemental metal or metal alloy of higher electrode potential which constitutes the second constituent of the composition is preferably selected from the group consisting of Mg, Al, Zn and Cd and their alloys. These metals and others are oxidized when brought into ionic contact with the compounds (1) described above in the presence of a suitable electrolyte.

Both the metal or alloy and the metal compound are dispersed in a binder (5) such as hydroxyethyl cellulose (Hercules N-lOO Ethoxy] 48) in which they aredistributed as finely divided powders. It appears that in the reactions in this invention, the binder reacts with strong electrolytes and in presence of active metals C-C and C-H bonds are broken and the organic matter of the binder may be decomposed into CO and H 0. The de composition of the binder is accompanied by partial deoxidation of the metal surface.

Consequently, the organic binder, in presence of metallic elements and upon action of a strong electrolyte, forms a fuel-cell wherein the organic matter supplies carbon which is converted into CO, at the anode while oxygen is reduced at the cathode and in its nascent state is absorbed at the anode.

Anode C 0 CO 4e Cathode O 30 4e 0 Total C 02 C02 The binder may be thinned to a suitable consistency by the addition of aromatic organic liquids (3), such as xylene or toluene diluted with propyl carbinol or methylated alcohol.

Finally, a small amount of paraformaldehyde is included in the composition in order to reduce overvoltage required for deposition of ionized metal in its elemental state.

When the composition has been deposited on the metal to be protected and is brought into contact with an electrolyte, elemental metals are oxidized while ionized metals are reduced to the elemental state in consequence of the electrolytic reaction.

At the time the ionized metal is reduced, it is capable of welding powdered metal particles at the moment of reduction from ionic state and the elemental metals which are in excess of the amounts used in the reaction are thus welded each to the other. Any porosity of the film is, therefore, eliminated by deposition of reduced and galvanized metal.

The elemental metal is provided in excess with reference to the reactions which take place and the resulting coating will contain one or two elemental metals with different electropotential, and higher than the electropotential of the ionized metals whereby reductionoxidation take place.

Further the elemental metals of higher electrode potential may be magnesium, magnesium-aluminum alloy 50:50 and zinc dust. These metals should be in very fine powder form.

The coating composition which is preferably a dispersion of elemental metals (2) of higher electrode potential-than the ionized metal in form of powders of very fine state of division and the ionized metals in form of oxides, carbonates or other organic compounds (1) in an organic binder (5) which may be ethyl cellulose in solution with xylene, toulene and alcohols, to which is added small percentage of paraformaldehyde, may be conveniently applied to the surface to be protected by brush, roller, spray-gun or dipping, i.e., immersion, or any other coating procedure.

The coating composition, after application, forms a dry film by simple evaporation of the solvents. The resulting coating is then post-treated by contact with an electrolyte containing metal ions such as zinc ion, stannic ion, lead ion or the like present in perchloric acid solution, acetic acid solution or hydrochloric acid solution, or other similar solution. Any of these electrolytes may be thickened by hydroxylethyl cellulose or similar compound to facilitate application as post-treatment of the coated surface.

Application of an electrolyte as a post-treatment places elemental metals into ionic contact with the metal compounds and results in an increase of temperature and hydrogen is liberated by metals of higher electrode potential. The products of oxidation are then expelled by hydraulic forces to the top of the coating film which produces an additional dehydrating protective layer.

The thickness of the deposited metallic film on the substrate may be conveniently increased by repetition of the coating and post-treatments.

Generally, the substrate does not require any special pre-treatment prior to the coating application, although the simple use of a wire brush to eliminate an excess of loose rust may be desirable.

The post-treatment should be applied only to the coating film after it has dried.

Instead of post-treatment by application of an electrolyte, the post-treatment also may be conveniently made by wire brush or rollers of elemental zinc, cadmium, lead, nickel or the like connected with an electrical source with controlled voltage and amperage in such way and manner whereby the elemental metal wire brush or roller by appropriate connection is either anodic or cathodic to the substrate.

It is also possible to use electrically connected wire brushes for cleaning the surface prior to the coating application. When used in post-treatment with electrolyte, the wire brushes reinforce film deposition by simultaneous electro-galvanization.

Although applicant does not wish to be bound with any of the theoretical explanations of the manner in which the substrate is protected against corrosion by deposition of the ionised metals in the metallic film to be formed on the metal substrate, it appears that firstly the coating is applied over the surface and forms an electrode. The coating film is a porous electrode composed of elemental metals of higher electrode potential than the ionised metals and the substrate. When posttreated by an electrolyte containing aquo metal ions penetration of the electrolyte into the porous film of the coating occurs and the elemental metals are placed into ionic contact causing transfer of metal electron valence or oxidation-reduction reaction resulting in oxidation of the elemental metals and the reduction of ionised metals. The protection of the substrate is achieved by the presence of elemental metal of higher electrode potential than the metal substrate and the reduced metal. During the reaction, the oxidation product is expelled from the metal coating and the pores in the deposited film are filled by newly reduced metal which galvanizes on the metal particles which are in excess welding the metallic particles to each other. During the reactions which take place, the organic binder is decomposed into CO and a perfect contact between the deposited metallic film and the metal substrate is established.

The invention is particularly suitable for anticorrosivc protection of iron or steel construction of bridges and the like.

The following are exemplary formulations which have been utilized in providing corrosion protection to iron and steel articles, the modes of application being as described in the preceding description.

EXAMPLE 1 A coating composition having the following percentages by weight:

-Continued By Weight Magnesium aluminium alloy powder (50:50) about 2.8 Zinc metal dust about 25.0 Lead monoxide about 22.00

Electrolyte for the post-treatment for the above coating:

1: By Wcight Perchloric acid solution (60% HCLO about 15.0% Lead perchloride about 15.0 Hydroxyethyl cellulose about 7.0 Water about 63.0

EXAMPLE 2 Coating composition:

% By Weight Ethyl cellulose about 14.0% Paraformaldehyde about 2.2 Xylene about 18.0 Propyl-carbinol about 16.0 Magnesium metal powder (pure) about 6.4 Zinc metal dust about 17.0 Zinc carbonate about 26.4

Electrolyte for post treatment:

% By Weight Perchloric acid solution (60% HCLO about 15.0% Zinc perchlorate about 15.0 Hydroxyethyl cellulose about 7.0 Water about 63.0

EXAMPLE 3 Coating composition:

% By Weight Ethyl cellulose about 14.0% Hydroquinone monobenzyl ether about 4.3 Paraformaldehyde about 2.2 Toluol about 18.0 Methylated spirit about 16.0 Magnesium aluminium alloy (50:50) about 3.5 Zinc metal dust about 42.0

Electrolyte for post treatment:

b By Weight Perchloric acid solution about 15.0% Stannic perchloride about 15.0 Hydroxyethyl cellulose about 7.0 Water about 63.0

Furthermore, the electrolyte may comprise any acid containing aquo metal ions in its solution.

It is to be understood that the coating composition may have beside elemental metal any ionised form of metals to be reduced, dispersed in a binder such that upon action of any acid solution reduction-oxidation reaction occurs in the coating itself.

I claim:

1. A method of protecting iron or steel structure from corrosion, in which a metallic protective film is provided on the iron or steel substrate to be protected, which comprises:

applying to the metal surface to be protected a paint consisting essentially of l. at least one elemental metal of higher electrode potential than the iron or steel to be protected,

2. at least one metal compound capable of yielding metal ions which are of lower electrode potential than the iron or steel to be protected or the said elemental metal and which are reducible by contact with one of said elemental metals, and

3. a vehicle for said constituents (l) and (2) comprising an organic binder permitting said composition to dry as a paint film on said structure and thereafter bringing said dried film into contact with an acidic aqueous electrolyte containing at least one of said metal ions whereby at least some of said elemental metal is oxidized and at least some of said metal compound is reduced to elemental metal and is deposited in said paint film.

2. A method according to claim 1, in which the metal compound capable of yielding metal ions in said coating composition is selected from the group consisting of zinc, cadmium, tin, lead, nickel and titanium in the form of perchlorates, chlorates, chlorides, acetates, carbonates, oxides and organic compounds, of said metals.

3. A method according to claim 1, in which the elemental metal of higher electrode potential is a finely divided powder of metal selected from the group consisting of magnesium, aluminium, zinc, cadmium and alloys of said metals.

4. A method according to claim I, in which the elemental metals are in excess to the reduction-oxidation reaction.

5. The method of claim 1 wherein the paint applied is thickened by ethyl cellulose to form coating suitable for application.

6. A method according to claim 1, in which the metallic film is formed on the substrate by metal ions deposition capable of welding" elemental metal of higher electrode potential than the substrate to form protective metallic film.

7. The method of claim 1 in which the electrolyte contains ions of at least one metal selected from the group consisting of zinc, tin and lead, in an acid solution.

8. The method of claim 7 in which the acid solution is a solution of an acid selected from the group consisting of perchloric, acetic and hydrochloric.

i 0 I t 

2. A method according to claim 1, in which the metal compound capable of yielding metal ions in said coating composition is selected from the group consisting of zinc, cadmium, tin, lead, nickel and titanium in the form of perchlorates, chlorates, chlorides, acetates, carbonates, oxides and organic compounds, of said metals.
 2. at least one metal compound capable of yielding metal ions which are of lower electrode potential than the iron or steel to be protected or the said elemental metal and which are reducible by contact with one of said elemental metals, and
 3. a vehicle for said constituents (1) and (2) comprising an organic binder permitting said composition to dry as a paint film on said structure and thereafter bringing said dried film into contact with an acidic aqueous electrolyte containing at least one of said metal ions whereby at least some of said elemental metal is oxidized and at least some of said metal compound is reduced to elemental metal and is deposited in said paint film.
 3. A method according to claim 1, in which the elemental metal of higher electrode potential is a finely divided powder of metal selected from the group consisting of magnesium, aluminium, zinc, cadmium and alloys of said metals.
 4. A method according to claim 1, in which the elemental metals are in excess to the reduction-oxidation reaction.
 5. The method of claim 1 wherein the paint applied is thickened by ethyl cellulose to form coating suitable for application.
 6. A method according to claim 1, in which the metallic film is formed on the substrate by metal ions deposition capable of ''''welding'''' elemental metal of higher electrode potential than the substrate to form protective metallic film.
 7. The method of claim 1 in which the electrolyte contains ions of at least one metal selected from the group consisting of zinc, tin and lead, in an acid solution.
 8. The method of claim 7 in which the acid solution is a solution of an acid selected from the group consisting of perchloric, acetic and hydrochloric. 